If you have a test light or multimeter, use it to find out where you're losing power. Remove your door panel, unplug the speaker, and place the leads from the multimeter/light into the positive and negative terminals of the connector for the speaker.
If you have power there, the issue is likely the speaker itself. If you don't have power there, head to the factory Bose amp. Find the wires that are the same color as the ones you just checked, and use the multimeter/light again. If you have power at the amp, then you have an issue with the wiring somewhere. If there's no power at the amp, it's probably an internal issue with the amplifier.
If you don't have a multimeter or test light, use the method mentioned in the post above me. If switching speakers makes sound, then your speaker is bad and you just need to replace it. If it doesn't, then you'll probably need a multimeter to track down where you're losing current.
